1. Field of the Invention
The present invention relates to a valve actuating apparatus for intake and exhaust valves in an internal combustion engine. More particularly, it relates to a valve actuating apparatus which can render only a predetermined intake and/or exhaust valve or valves inoperative at a given engine condition.
2. Description of the Related Art
In a multi-cylinder internal combustion engine, it is known to selectively render only predetermined intake or exhaust valve(s) inoperative in order to cancel out the associated cylinder(s), thereby controlling the total displacement of the effective cylinders, in accordance with the engine load, resulting in the realization of a variable-cylinder internal combustion engine.
Among known valve actuating apparatuses of the kind mentioned above, those closest to the present invention are disclosed, for example, in Japanese Unexamined Utility Model Publication (Kokai) Nos. 59-68109 and 59-67506, in which a rocker arm is divided into two rocker arm elements, one of which bears against a cam and the other bears against a valve stem of the associated intake or exhaust valve. These two arms are interconnected by means of a connecting shaft for relative sliding rotation. The relative sliding rotation takes place between the two arms when only a predetermined intake or exhaust valve is made temporarily inoperative, to absorb the valve lift of the associated valve. The two arms are provided with male and female engaging members which are selectively engaged and disengaged. One of the male and female members can be actuated by an actuator, such as a solenoid means, to selectively occupy locked and unlocked positions.
However, in the known apparatuses mentioned above, there is a possibility that when the associated valve is actuated by the rocker arm, the cam may come into contact with the first arm which is supported by the rocker arm shaft. In this case where the cam comes into contact with the first arm, the rotation of the cam is transmitted first to the first arm and then to the second arm, which bears against the valve stem, by means of the connecting shaft. As a result, a large cam force is exerted on the connecting shaft, and accordingly, a large connecting shaft must be provided and also wear of the connecting shaft is increased by the resultant large frictional force applied thereto.
Furthermore, when the rocker arm is in an inoperative position, in which the two rocker arms are rotated or inclined relative to each other, there is a possibility that the cam will come into partial contact with the first arm. Generally speaking, the second arm, which bears against the valve stem, has a cam contact surface, i.e., an upper surface, which bears against the cam and which is usually subjected to a surface treatment for increasing the friction resistance thereof, such as hardening or quenching, but the upper surface of the first cam is not usually subjected to such a surface treatment; because the first arm comes into partial contact with the cam only when the relative inclination or relative rotation takes place between the two arms of the rocker arm, and accordingly, there is less necessity for a surface treatment of hardening the first arm, in comparison with the second arm, and because it is very difficult to partially harden or quench only the desired portion of the upper surface of the first arm that comes into contact with the cam. Since the surface treatment is expensive, hardening or quenching of entire first arm is not practically acceptable.
Furthermore, in the known apparatuses mentioned above, there is a problem in that the rocker arm tends to interfere with a valve stem of an adjacent valve unit (valve, valve stem, valve retainer, etc.), since the valve units are located very close to each other in a multi-cylinder internal combustion engine. Namely, the first arm of the rocker arm when relatively inclined to the second arm tends to interfere with the valve retainer of an adjacent valve unit. This interference can be solved by decreasing the angular displacement of the first arm (or the second arm).